The New Jersey Median Barrier is the tapered concrete barrier that is used
in many narrow highway medians, to prevent vehicle crossovers into oncoming traffic.

Sources: A report from the Transportation Research Board, National Research
Council. The report is called NCHRP Synthesis 244, "Guardrail and Median
Barrier Crashworthiness", published in 1997. Chapter 5 is about concrete
median barriers.

A quote from the text, "Although it is not clear exactly when or where the
first concrete median barriers were used, concrete median barriers were used in
the mid-1940s on US-99 on the descent from the Tehachapi Mountains in the central
valley south of Bakersfield, California. This first generation of concrete barriers
was developed to (a) minimize the number of out-of-control trucks penetrating
the barrier, and (b) eliminate the need for costly and dangerous median barrier
maintenance in high-accident locations with narrow medians -- concerns that are
as valid today as they were 50 years ago".

The first concrete median barrier used in New Jersey was installed in 1955,
and it was only 18 inches tall. It looked like a low vertical wall with a curb
on each side. Operational problems were observed, the shape was changed, and the
height was increased to 24 inches, and to 32 inches in 1959. The commonly seen
shape came into being then. Basically, going upward, the first 2 inches from the
pavement rises vertically, the next 10 inches rises at a 55-degree angle, and
the remainder at an 84-degree angle (as measured from horizontal).

New Jersey did not use crash-testing to develop the barrier. The state highway
department observed the accident results of its barrier installations, and evolved
the shape of the barrier. Both New Jersey and California continued experimenting
in the early 1960s, and the New Jersey barrier was widely adopted by California;
they installed 132 miles by 1972 and 680 miles by 1988. The barrier's use has
expanded to nearly every state since then.

Actually there are six different concrete median barrier designs, although
the New Jersey barrier is the most-used design. It should also be mentioned that
these same shapes are commonly used on single-faced roadside barriers, such as
bridge parapets, tops of retaining walls in fill sections, and barriers against
rock cuts.

The Ontario tall-wall barrier has the same slopes as the New Jersey barrier,
but it is 42 inches high. The F-shape barrier is similar to the New Jersey barrier,
but bottom section is lower and the slope a bit flatter. The Constant-slope barrier
is 42 inches high, and the sides have a single slope of 79 degrees. The Constant-slope
barrier is the latest concept, and was developed using crash-testing. About a
mile of this barrier was installed on I-95 in Virginia just north of the I-295
interchange north of Richmond.

The report mentions the GM barrier, and says that it is now considered obsolete.
General Motors developed the GM barrier in conjunction with the Texas Transportation
Institute in the early 1970s. It looks similar to the New Jersey barrier, but
looks fatter. The slope breakpoint is about 3 inches higher. The shape was developed
by crash testing, and at a time when cars were large.

The basic reason for the New Jersey profile is to redirect a vehicle that hits
it. The vehicle's wheels and sheet metal on the impacting side ride upward to
prevent vehicle rollover. I remember the photos in the report, and cars, trucks
and busses alike were redirected. Jersey Barrier is very heavy, something like
600 lbs. per linear foot of barrier. Often, it is cast-in-place or slipformed
onto a concrete footer with steel dowel anchors. A tractor-trailer impacting at
a 15-degree angle at 60mph will be successfully redirected. The cost per linear
foot of New Jersey Barrier is two to three times the cost of a steel guardrail
median barrier.

Virginia used the GM barrier until about 1979 or so. The I-495 Capital Beltway
widening 1974-1977 used this. The I-395 Shirley Highway reconstruction from King
Street to the Potomac River, 1969-1975, used it. Several miles of I-95 in South
Richmond used it when the road was widened 1974-1978. Virginia Interstate widening
and median barrier projects since then have used the New Jersey barrier. Notice
the recent I-95 widening from Springfield to Woodbridge, and the 1980s median
barrier replacements on I-95 in the Richmond-Petersburg area; they used New Jersey
barrier.

The GM barrier was designed at a time when cars were significantly larger.
The New Jersey barrier has a lower slope breakpoint, and it looks more compatible
with the smaller cars that became evident around 1980 or so.

After having written this article in November 1997, I have in December 2000
found this link in Public Roads Magazine, March-April 2000,
Basics of Concrete Barriers by Charles F. McDevitt,
a structural engineer in the Federal Highway Administration's Office of Safety
Research and Development at the Turner-Fairbank Highway Research Center in McLean,
Va. For the last 22 years, he has worked on developing new and improved traffic
barriers. He discusses the various concrete median barrier types, and the article
has technical diagrams of the barriers. From his report, "Conclusion: Each of
these concrete barrier types fills a niche and helps meet the needs of highway
agencies that select, design, and locate traffic barriers. In terms of safety
performance, the 1070-mm (42-in) F-shape is currently our best technology. The
F-shape profile is clearly superior to the NJ-shape and is gradually being used
by more states for both portable concrete barriers and permanent barriers".

The current (1998-2001)
six-lane widening project on 9 miles of VA-150 Chippenham Parkway in Richmond,
Virginia, has used a 42-inch-high F-shape Barrier.